1. Field of the Invention
The present invention relates to methods for adjusting voltage control type oscillators. More particularly, the present invention relates to methods for adjusting the frequencies and control-voltage sensitivities of voltage control type oscillators including microstrip line resonators.
2. Description of the Related Art
For example, as shown in FIG. 2, in a conventional voltage control type oscillator 1 including a microstrip line resonator, a strip electrode 3 is provided on a first surface of a dielectric substrate 2, and a ground electrode 4 is provided on a second surface of the dielectric substrate 2. In the voltage control type oscillator 1, in addition to a resonator defined by a microstrip line, electronic components 5 are mounted on the first surface of the dielectric substrate 2. In order to adjust the frequency and control voltage of the voltage control type oscillator 1, the strip electrode 3 is trimmed. In this case, trimming is performed by irradiating a laser beam on the strip electrode 3. In this manner, after trimming the strip electrode 3, a case for covering the strip electrode 3 and the electronic components 5 is attached to the dielectric substrate 2.
In addition, in FIG. 3, there is shown another conventional voltage control type oscillator including a microstrip line resonator disposed on a multi-layer substrate. In a voltage control type oscillator 1, a strip electrode 3 is disposed inside a dielectric substrate 2. Then, two ground electrodes 4 and 6 are arranged to sandwich the strip electrode 3 therebetween. Like the ground electrode shown in FIG. 2, the ground electrode 4 is disposed on the second surface of the dielectric substrate 2. The ground electrode 6 is disposed inside the dielectric substrate 2. Electronic components 5 are mounted on the first surface of the dielectric substrate 2, and a case 7 is attached to the dielectric substrate 2 such that the case 7 covers the electronic components 5. In this voltage control type oscillator 1, after attaching the case 7, trimming of the strip electrode 3 is performed. In this case, a laser beam is irradiated from the second surface side of the dielectric substrate 2 to trim the strip electrode 3.
However, as shown in FIG. 2, when trimming the strip electrode from above, since the case 7 is attached after the trimming, a magnetic-field change occurs, thereby causing changes in various characteristics including frequency characteristics. In addition, depending on the state in which the case 7 is attached, there are generated variations between the characteristic changes, which increases variations in the characteristics between produced voltage control type oscillators.
In addition, as shown in FIG. 3, when attaching the cover on the first surface of the multi-layer substrate having a circuit disposed thereon and trimming the strip electrode from the second surface side of the multi-layer substrate, the distances between the strip electrode disposed inside the multi-layer substrate and the ground electrodes sandwiching the strip electrode therebetween are narrow. Thus, noise characteristics such as C/N characteristics (carrier/noise ratio) are deteriorated. Furthermore, in the case of the multi-layer substrate, a substrate material cost is higher than the case using the dielectric substrate having the strip electrode disposed thereon.
In order to overcome the problems described above, preferred embodiments of the present invention provide a method for adjusting a voltage control type oscillator that prevents characteristic changes occurring after adjustments and permits the voltage control type oscillator to be produced at a low cost.
According to a preferred embodiment of the present invention, a method for adjusting a voltage control type oscillator includes the steps of forming a strip electrode on a first surface of a dielectric substrate, forming a ground electrode on a second surface of the dielectric substrate, providing a case which covers the strip electrode on the first surface of the dielectric substrate, and trimming the strip electrode from the second surface side of the dielectric substrate after the case is provided.
In addition, in the method for adjusting the voltage control type oscillator, the strip electrode may be trimmed by a laser.
By using a microstrip line resonator including the strip electrode provided on the first surface of the dielectric substrate and the ground electrode provided on the second surface thereof, the substrate material cost is much lower than the case of the multi-layer substrate. In addition, since the method can widen the distance between the strip electrode and the ground electrode, the voltage control type oscillator can have satisfactory characteristics.
Furthermore, trimming is performed from the second surface side of the dielectric substrate after the case is provided on the first surface of the dielectric substrate. That is, since the cover is not attached after adjustments, this arrangement can prevent characteristic changes occurring after adjustments.